Firstly, in case you don't know, Dropbox is a cross-platform service for file sharing, synchronizing and backup. The application is free, along with basic use of the service (up to a limit of 2GB). However, by referring users to create a Dropbox account, both the user who is referring and the user who created the account get 250 MB extra space. Referring users allows you use up to 5 GB of space for free.

And now, about using Multiple Dropbox instances (and obviously, multiple accounts) in the same time. Yes, there is a way to run multiple Dropbox instances on the same computer. Here is how:

1. For Windows, see this tutorial (I haven't tested it on Windows yet).

2. For Linux, run the following command in a terminal:

HOME=$HOME/.dropbox-alt /usr/bin/dropbox start -i

This will launch the Dropbox initial setup for the folder called .dropbox-alt which does not exist, so you'll be presented with the initial configuration. You can create a new account or use an existing one.

If you already had a Dropbox instance running, now there should be 2!

To run this second Dropbox instance at startup, paste the following command in a terminal:

sudo gedit /etc/rc.local

And paste the following line just before the "exit 0" last line:

su username -c "HOME=$HOME/.dropbox-alt /usr/bin/dropbox start"

If the file doesn't have "exit 0" on the last line, add it yourself. Basically, this is how the last two lines in the /etc/rc.local file should look like:

Note 1: the instructions for Mac OSX also include instructions for Linux but the Linux instructions are not entirely correct, so for Linux, use the instructions in this post!

Note 2: It seems you cannot login to the Dropbox website when running multiple Dropbox instances. However, by right clicking the Dropbox icon in the notification area and selecting "Launch Dropbox Website", you will be automatically logged in.

Note 3: Using the Dropbox link on top of the post to create a Dropbox account, you will get an extra 250 MB for your account; I will also get an extra 250 MB.